Metallic parts tend to be heavy due to the high densities of most metals. Typically, there are areas of a metallic part that are lightly loaded or not loaded (little or no stress) as well as highly loaded (or stressed) areas. An ideal metallic part would contain a sufficient amount of metal in high-stress areas to transmit the necessary loads and perform the function of the part. Such an ideal part would also contain less or no metal in areas with little or no stress, thereby reducing the weight of the metallic part to an idealized minimum. In some cases, removing metal from a metallic part can lead to weight savings. However, removing metal from a metallic part by conventional means, such as machining, laser drilling, etc., can be both difficult and costly. Further, removing material from a metallic part can lead to reduced material properties of the part, which may be unacceptable for its intended application. Therefore, there is a need for improved and/or lower-cost methods of producing metal parts that are lightweight but strong enough in high-stress areas to perform the function(s) of the part.
There is an ongoing effort to replace metal components in a gas turbine engine with lighter components made from alternative materials, even if the components experience significant loads or are subjected to environmental concerns (e.g., high or low temperatures, erosion, foreign-object damage) during use. For example, in the aerospace industry, manufacturers of gas turbine engines are considering the use of alternative materials for fan blades, compressor blades, and possibly turbine blades. Suitable non-metal alternative materials include, but are not limited to, reinforced polymers, polymer matrix composites, ceramics, and ceramic matrix composites.
Blow molding processes begin with melting the molding material and forming it into a parison or preform. The parison is a tube-like piece of plastic with a hole in one end through which compressed air can pass through. The parison is clamped into a mold and air is pumped into the parison. The air pressure pushes the molding material outwards to match the interior surface of the mold. Once the molding material has cooled and hardened, the mold opens and the part is ejected. In contrast, injection molding includes injecting molding material for the part into a heated barrel, mixing and forcing the molding material into a mold cavity where the molding material cools and hardens to the configuration of the cavity. Compression molding is a method of molding in which the preheated molding material is placed in an open-mold cavity. The mold is closed and pressure is applied to force the material into contact with all mold areas while heat and pressure are maintained until the molding material has cured.
For many molding processes, hard tooling is used to form the mold or die. While hard tooling can provide high dimensional repeatability, hard tooling is very heavy and cumbersome and can present a safety hazard when moved or handled. Further, fabricating hard tooling is time consuming and costly. As a result, hard tooling is normally too expensive and time consuming for short production runs and/or for the fabrication of test parts. Thus, the ability to quickly fabricate tooling to support short production runs and/or test runs of composite materials is desired.
Blow molding and injection molding cannot be used if the plastic to be molded is in the form of a composite with a plurality of layers or plies, i.e., a composite layup structure. Composites are materials made from two or more constituent materials with different physical or chemical properties that, when combined, produce a material with characteristics different from the individual components. The individual components remain separate and distinct within the finished structure. Typically, composite layup structures can be molded or shaped using compression molding, resin transfer molding (RTM), or vacuum assisted resin transfer molding (VARTM), all of which utilize hard tooling that typically include details machined into one or more blocks of metal that form the mold.
Composites can also include reinforcing fibers or matrices. The fibers or matrices may be formed from ceramics, metals, polymers, concrete, and various other inorganic and organic materials. Organic matrix composites (OMCs) may include polyimides and/or bismaleimides (BMIs) because they can be used at higher temperatures than other commonly used organic reinforcing materials, such as epoxies. Such high-temperature OMCs may be processed by autoclave molding, compression molding, or resin-transfer molding. These processes all require lengthy cure and post-cure cycles as well as hard tooling that is difficult and costly to make. Thus, improved methods for molding OMCs are also desired.
Electrolytic and electroless plating are inexpensive methods of forming a metallic layer on a surface of a molded plastic article. To ensure adhesion of the plated layer to the molded plastic article, the surface of the plastic article may need to be prepared by etching, abrading, or ionic activation. The most common types of metals used for plating molded plastic include copper, silver, and nickel, although other metals may be used.
Electrolytic plating is the deposition of a metal on a conductive material using an electric current. A molded plastic article must first be made conductive to be electrolytically plated. This can be done through a multi-step process that typically involves the application of a catalyst, electroless plating of Ni, and electrolytic plating of Cu. The article to be electrolytically plated is then immersed in a solution of metal salts connected to a cathodic current source, and an anodic conductor is immersed in the bath to complete the electrical circuit. Electric current flows from the cathode to the anode, and the electron flow reduces the dissolved metal ions to pure metal on the cathodic surface. Soluble anodes are made from the metal that is being plated and dissolve during the electroplating process, thereby replenishing the bath.
A closely related process is brush electroplating, in which localized areas or entire items are plated using a brush saturated with plating solution. The brush may be a stainless steel body wrapped with a cloth material that both holds the plating solution and prevents direct contact with the item being plated. The brush may be connected to the positive side of a low-voltage direct-current power source, and the item to be plated connected to the negative side. The operator dips the brush in plating solution then applies it to the item to be plated, moving the brush continually to get an even distribution of the plating material. Brush electroplating has several advantages over tank plating, including portability, ability to plate items that for some reason cannot be tank plated (e.g., plating portions of very large decorative support columns in a building restoration), low or no masking requirements, and comparatively low plating solution volume requirements. Disadvantages compared to tank plating can include greater operator involvement (tank plating can frequently be done with minimal attention), and inability to achieve a plate as thick as can be achieved using tank plating.
Measuring strain on rotating components has historically been problematic and involves sending data out to stationary data acquisition systems via split-ring electrical coupling or radio frequency (RF) transmission devices. Strain gages, the associated wiring, and/or the mass and volume of a radio transmitter can interfere with the operation of a component, especially if balancing is critical, if the space envelope surrounding the component is tight, or if airflow over a surface of the component is involved. Measuring strain on rotating components is important to accurately assess component failure, whether it is made from a traditional alloy or from an aforementioned alternative material.
Plated polymeric mechanical test specimens are needed to accurately characterize the stress and strain imposed on a plated polymeric structure. Test specimens that are completely encapsulated in metal plating are not preferred because such an encapsulated specimen does not simulate a semi-infinite medium, which best approximates plated polymer walls in actual parts. It is more helpful to cut test specimens out of larger plated panels to provide exposed edges (a sandwich structure) approximating a semi-infinite medium. Preliminary testing of plated polymers demonstrates that tensile testing of thick-plated polymers cannot be reliably accomplished by gripping standard test specimen geometries, such as the test specimens specified by ASTM D638. Gripping a standard, plated test specimen results in either (1) too much slippage to accurately or reliably calculate ultimate load, displacement, and strain values, or (2) the test specimen being crushed in the grip region, resulting in stress concentrations, significant strain outside of the gage area, and premature failure.
Therefore, there is a need for improved methods and apparatuses for measuring strain imposed on parts, including rotating components, that may be made from alternative materials such as polymers, reinforced polymers, polymer matrix composites, ceramics, and ceramic matrix composites.